1. Field of the Invention
The present invention relates to an optical element used for a sensor such as a CCD and CMOS, and particularly relates to an optical element and a method of molding the same whereby a ghost is prevented.
2. Description of the Related Art
In recent years, as compact digital cameras mounted in mobile telephones or the like have increased in functionality and accuracy, higher accuracy is demanded of small sensor lenses used for the digital cameras.
FIG. 1 shows the configuration of a lens using a sensor (including a CCD and CMOS) of a compact digital camera mounted in a mobile telephone or the like.
In a sensor lens 100 of FIG. 1, first to third optical elements 101 to 103 are fixed to a lens-barrel 105 with adhesive 104 and the optical elements with the lens-barrel are mounted in a mounting holder 106 which has a cover glass 107. In the sensor lens 100, light incident from a condensing port 105a of the lens-barrel 105 converges through the first to third lenses 101 to 103 and an image is formed on a sensor image-forming surface 108.
For example, an optical element used for a sensor lens includes a glass grind lens, a glass molded lens, and a plastic lens. Such an optical element is constituted of an optical function surface of high surface accuracy and a flange formed around the surface.
In the sensor lens using the optical element composed of the optical function surface of high surface accuracy and a flange formed around the surface, the sensor image-forming surface is adversely affected by the scattering of light having been incident outside the optical function surface of the optical element, resulting in a ghost or flare. For example, unexpected light (scattered light) is caused by internal reflection in the optical element and a mechanical part such as a lens-barrel. The scattered light reaches the sensor image-forming surface and causes a ghost or flare. A sensor lens is known which comprises a stopper 109 for interrupting the entry of scattered light into a sensor image-forming surface, the scattered light having been caused by a light beam incident outside an optical function surface, e.g., on a flange, so that a ghost or flare caused by the scattered light is prevented (e.g., Japanese Utility Model Laid-Open No. 2-107111 and Japanese Patent Laid-Open No. 2003-298885).
However, even in the sensor lens comprising the stopper 109 for interrupting scattered light caused by light having been incident outside the optical function surface, e.g., on the flange, it is not possible to completely eliminate a ghost. Further, as compact digital cameras have increased in functionality and accuracy, just a small ghost seriously affects the function and accuracy.
A solution for preventing such a small ghost is to reduce the interior diameter of the stopper 109. However, when the stopper 109 is reduced in internal diameter, a peripheral luminous flux decreases in light quantity as compared with a central luminous flux, thereby darkening the corners of an image.